The present disclosure relates to an image forming apparatus which forms an electrostatic latent image on an image bearing member by scanning light emitted from a light source in a main scanning direction of the image bearing member using a rotary polyhedron.
An electrophotographic image forming apparatus forms an electrostatic latent image on a photoconductive drum by reflecting light emitted from a light source by a polygon mirror (rotary polyhedron) being driven and rotated and scanning it in a main scanning direction of the image bearing member. The polygon mirror has a plurality of reflecting surfaces formed of reflecting mirrors and reflects light by each reflecting surface to scan the rotating photoconductive drum in the main scanning direction. At this time, if the inclination of each reflecting surface with respect to a rotary shaft of the polygon mirror is equal, pitches between lines drawn by the respective reflecting surfaces (line pitches in a sub scanning direction which is a rotating direction of the photoconductive drum) are constant.
However, pitches between lines drawn by the respective reflecting surfaces of the polygon mirror may vary due to a variation of the inclination of the respective reflecting surfaces with respect to the rotary shaft (optical face tangle error) such as caused by a variation of processing accuracy and vibration associated with high-speed rotation of the polygon mirror. As a result, pitches between horizontal lines in a formed image vary in the case of using image data composed of a plurality of horizontal lines at equal intervals. Thus, there has been a problem of being unable to obtain an image with good quality.
As a conventional technology, there is known a method for correcting an optical face tangle error in a main scanning direction while specifying reflecting surfaces of a polygon mirror. However, this method is effective in aligning writing positions in the main scanning direction, but cannot correct line shifts in a sub scanning direction, wherefore it has not been possible to suppress image quality deterioration.
An object of the present disclosure is to provide an image forming apparatus and an exposure method capable of suppressing quality deterioration of a formed image even when an optical face tangle error of a rotary polyhedron is present.